JPH0562868A - Substrate provided with etching monitor - Google Patents

Abstract

(57) [Summary] [Purpose] Even when etching a part that cannot be confirmed from the outside, it is possible to visually and accurately grasp the actual progress of the etching that is currently in progress. [Structure] On one surface of a semiconductor substrate 1, a monitor layer 3 and a transparent etching-resistant protective layer 4 which are made of a substance having the same quality as the etching target portion of the substrate 1 or a known etching rate ratio are observed from the outside. The layers are laminated as possible and at least one end surface 3a of the monitor layer 3 is exposed from the protective layer 4. Since the monitor layer 3 is etched according to the etching rate of the etching target portion, the etching progress of the etching target portion can be grasped by observing the etching amount of the monitor layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate provided with an etching monitor capable of visually observing the etching depth when manufacturing a semiconductor device or the like.

[0002]

2. Description of the Related Art For example, when manufacturing a semiconductor device, various etching processes are indispensable, and the etching amount is conventionally controlled as follows. First, FIG. 5A shows a case where the (100) Si semiconductor substrate 1 is etched to a desired depth using a mixed solution of hydrofluoric acid and nitric acid.
FIG. 2B shows an example in which the substrate is laterally etched using a basic solution such as an aqueous potassium hydroxide solution.
In the figure, 2 is a mask material having resistance to an etching solution. In such a case, the etching depth is generally confirmed by measuring the level difference d including the mask material 2 using a level difference measuring device after the etching is completed.

On the other hand, as shown in FIG. 2, it is necessary to laterally etch the side wall of the deep groove (trench) 1A formed in the (100) Si semiconductor substrate 1 by d using a basic etching solution. Sometimes, but in this case, substrate 1
The etching shape cannot be confirmed from the surface of the.
Therefore, a method of measuring the etching rate in advance and estimating the etching shape from the etching time based on this is used.

[0004]

However, the former of the above-mentioned conventional examples cannot measure the depth thereof during the progress of etching. Further, since the thickness of the mask material 2 is measured, the measured value lacks reliability due to the influence of the change in the thickness of the mask material 2. Further, there is a problem that it is generally impossible to measure the step difference in etching having a large aspect ratio (aspect ratio) of the groove, such as the case of forming the trench.

In the latter case, when the etching rate is likely to change due to changes in the composition of the etching solution during etching, delicate agitation, temperature changes, etc., even if the etching time is adjusted, the actual processing shape However, there is a problem in that it is difficult to confirm this during etching.

It is an object of the present invention to provide a substrate with an etching monitor that enables the user to visually and accurately grasp the actual etching situation that is actually proceeding even when etching a portion that cannot be confirmed from the outside.

[0007]

To explain with reference to FIG. 1 showing an embodiment, a substrate with an etching monitor of the present invention is the same as or different from the substance constituting the etching target portion of the substrate 1. However, a monitor layer 3 made of a substance having a known etching rate ratio of both is formed on one surface of the substrate 1, and the monitor layer 3 is covered with a transparent protective layer 4 having etching resistance. At least one of
The end surface 3a is exposed from the protective layer 4.

[0008]

When the target portion of the substrate 1 is etched, the monitor layer 3 is laterally etched from the end face 3a exposed from the protective layer 4. By observing the progress through the transparent protective layer 4, it is possible to know the actual progress of etching at the etching site. In addition,
In the section of means and action for solving the above problems for explaining the configuration of the present invention, the drawings of the embodiments are used to make the present invention easy to understand, but the present invention is limited to the embodiments. is not.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an example of the configuration of an etching monitor suitable for use in a process of forming an SOI structure by etching the inside of a (100) Si semiconductor substrate 1, and FIG.
Is a plan view, and FIG. 6B is a bb sectional view thereof. Next, the forming method will be described.

In the above process, a poly-Si layer having a thickness of several thousand Å is formed on an unnecessary region of the semiconductor substrate 1 to be etched, that is, on a scribe line other than the element forming region, and then this poly-Si layer is formed. Is processed into a strip shape having a width of several μm and a length of several tens of μm by using a photoetching method to form a poly-Si film 3 to be a monitor layer. At this time, P or N type impurities may be diffused in the poly-Si film 3, or heat treatment may be performed after processing.

Next, a PSG film 4 serving as a protective layer is formed by the CVD method or the like, and a part thereof is removed by photoetching to expose one short side 3a of the poly-Si film 3. At this time, the scale 5 may be carved on the surface of the PSG film 4, which is the protective layer, by photoetching.

Although only the monitor is shown in FIG. 1, a trench 1A is formed in the element forming region of the semiconductor substrate 1 as shown in FIG. The etching process is performed with a basic etching solution to a predetermined depth. The PSG film 4 has resistance to this etching solution. Also in this case,
Since the etching is performed in the lateral direction perpendicular to the sidewall of the trench 1A, that is, parallel to the surface (main surface) of the semiconductor substrate 1, the direction is (110).

Therefore, when actually performing the etching, the ratio of the etching rate of the basic etching solution to the (110) Si and the poly-Si film 3 is measured in advance under the same conditions. As a result, the depth of the etching that progresses laterally from the side wall inside the trench 1A, and the state of the etching that progresses from the short side 3a of the poly-Si film 3 arranged on the surface of the semiconductor substrate 1 can be observed with an optical microscope or the like. You can observe and know. That is, how much the poly-Si film 3 was removed from the short side 3a exposed from the PSG film 4 was measured through the PSG film 4 from the substrate surface,
The progress of etching in the lateral direction inside the trench 1A can be grasped from the etching amount.

This method does not directly measure the etching depth itself which progresses on the side wall of the trench 1A.
Scale the etching amount of the poly-Si film 3 on the surface of the semiconductor substrate.
Although it is measured relatively as a tool, etching progresses simultaneously under the same conditions with the same etching solution,
Since the influence of variations in conditions such as the composition and temperature of the etching solution is affected in the same manner, accurate measurement can be performed.

Further, since the change in the length of the poly-Si film 3 is known only by observing it from the surface of the substrate, it is possible to grasp the state of etching which is actually proceeding without interrupting the etching operation. In this case, if the scale 5 is engraved with a numerical value corresponding to the etching depth of (110) Si, the etching amount can be more easily grasped.

Although the case of performing the etching as shown in FIG. 2 has been described above, the etching monitor of the present embodiment is similarly effective when applied to the case of the substrate structure as shown in FIG. The substrate structure shown in FIG. 3 is used, for example, in an NPN vertical bipolar transistor.
0) N-type impurity high-concentration buried layer 6 on Si semiconductor substrate 1
Is formed, and an N-type epitaxial layer 7 is further formed thereon.
Are formed.

Here, it is assumed that the trench 8 having a depth reaching the buried layer 6 is formed, and only the buried layer 6 is selectively etched laterally from its sidewall by a desired depth. As the etching liquid, a solution obtained by mixing hydrofluoric acid, nitric acid, and acetic acid at a volume ratio of 1: 3: 8 is used.

In this case, N-type high concentration impurities are doped on the monitor poly-Si film 3 formed on the surface,
The ratio of the etching rate of the etching solution to the poly-Si film 3 and the buried layer 6 is measured in advance under the same etching conditions. Accordingly, in actual etching, the lateral etching depth of the buried layer 6 can be monitored by observing the lateral etching depth of the poly-Si film 3 from the surface.

Next, another embodiment will be described with reference to FIG.
The figure shows an N-type epitaxial layer 12 on a P-type semiconductor substrate 11.
Is shown, and the selective etching of the P-type semiconductor substrate 11 is performed while applying an anodic bias to the N-type epitaxial layer 12. The figure (a) is a plan view and the figure (b) is shown. Is a bb sectional view thereof.

An insulating film 13 such as an oxide film is formed on the N-type epitaxial layer 12 formed on the P-type semiconductor substrate 11, and a poly-Si film 14 serving as a monitor layer is formed thereon. The poly-Si film 14 includes a P-type poly-Si film 14a doped with P-type impurities and an N-type poly S doped with N-type impurities.
i film 14b.

Then, the N-type poly-Si film 14b and the N-type epitaxial layer 12 are brought into contact with each other to form an electrode 17 made of a metal such as Al, and then a PSG film 18 to be a protective layer is formed so as to cover the whole. Then, a part thereof is removed by photoetching to expose one short side 14c of the poly-Si film 14.

The etching is performed with a basic etching solution.
The mask material 19 is used to carry out from the back surface of the semiconductor substrate 11 to remove the inner hatching portion 16 of the pattern shown by the dashed line in the figure. At that time, an appropriate anode is used for the metal electrode 17.
When the etching is performed with the Dick bias applied, the etching automatically stops at the interface with the N-type epitaxial layer 12.

At this time, the short side 1 of the P-type poly-Si film 14a
By observing the amount of etching proceeding from 4c in the horizontal direction from the front surface, the etching depth in the vertical direction of the P-type semiconductor substrate 11 on the back surface can be monitored. If an appropriate bias is not applied, the N-type poly-Si film 14b is dissolved or the etching of the P-type poly-Si film 14a is stopped. Therefore, by observing this, an appropriate bias is applied. You can also check whether it is done or not. That is N
By setting the bias conditions so that the etching of the P-type poly-Si film 14a proceeds while the pattern of the poly-Si film 14b remains, high-precision etching is performed while maintaining a high process yield. be able to.

The former of the two embodiments described above is S
It can be easily applied to the manufacturing process of high-speed and high-frequency devices with high withstand voltage or low parasitic capacitance such as OI, and the latter is considered to be applied to micromachining processes such as sensors. However, of course, the present invention is not limited to these, and is always effective when it is desired to monitor the etching state inside or on the back surface of the substrate during the device process. In any of the embodiments, the monitor is installed in an unused area on the semiconductor substrate, for example, on the scribe line, so that the utilization efficiency on the substrate surface is not lowered.

Further, only the case of monitoring the etching of the side wall of the trench and the back surface of the substrate has been described. However, even if the etching of a predetermined depth from the surface of the substrate is performed as shown in FIG. 5, the monitor of the present invention can be used. However, there is an advantage that the depth can be measured with high accuracy without interrupting the etching. Although only the combination of the monitor layer of the poly-Si film and the protective layer of the PSG film has been described, the present invention is not limited to this. Further, although the etching of the semiconductor substrate has been described, the present invention can be applied as an etching monitor for other substrates.

[0026]

According to the present invention, since the monitor layer that is etched according to the etching amount of the etching target portion is provided on one surface of the substrate so that it can be observed, the etching operation can be performed without interruption. It is possible to visually and accurately grasp the etching condition of a certain etching target site, which improves the etching accuracy, prevents process errors such as insufficient etching and overetching, and ensures a high yield.

[Brief description of drawings]

FIG. 1 shows an etching monitor showing an embodiment of the present invention, in which (a) is a plan view thereof and (b) is a sectional view thereof.

FIG. 2 is a cross-sectional view showing a configuration example of a substrate to be etched.

FIG. 3 is a cross-sectional view showing another configuration example of the substrate.

FIG. 4 shows another embodiment, in which (a) is a plan view thereof and (b) is a sectional view thereof.

FIG. 5 is a cross-sectional view showing another configuration example of the substrate.

[Explanation of symbols]

 1, 11 Semiconductor substrate 3, 14 Monitor layer 3a made of poly Si film 3a Exposed short side of monitor layer 4, 18 PSG film 6 Buried layer 7, 12 N type epitaxial layer 8 Trench 14a P type poly Si film 14b N type poly Si film 14c Exposed short side of monitor layer

Claims (1)

[Claims] 1. A monitor layer is formed on one surface of a substrate, the monitor layer being made of a substance that is the same as or different from the substance that constitutes the etching target portion of the substrate but that has a known etching rate ratio between the two substances. A substrate with an etching monitor, characterized in that the monitor layer is covered with a transparent etching-resistant protective layer, and at least one end face of the monitor layer is exposed from the protective layer.